linux-kernel - Re: [PATCH 1/4] locking/rwsem: Add missing ACQUIRE to read

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Message-ID: <20190719084956.GA6750@andrea>
Date:   Fri, 19 Jul 2019 10:49:56 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Jan Stancek <jstancek@...hat.com>,
        Waiman Long <longman@...hat.com>, dbueso@...e.de,
        mingo@...hat.com, jade.alglave@....com, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/4] locking/rwsem: Add missing ACQUIRE to read_slowpath
 exit when queue is empty

> @@ -1032,6 +1032,8 @@ rwsem_down_read_slowpath(struct rw_semap
>  		 */
>  		if (adjustment && !(atomic_long_read(&sem->count) &
>  		     (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
> +			/* Provide lock ACQUIRE */
> +			smp_acquire__after_ctrl_dep();

Does this also make the lock RCtso?  Or maybe RCtso was already
guaranteed (and I'm failing to see why)?

Thanks,
  Andrea